Bisphenol-A is a feedstock or intermediate product for the commercial production of various polymers including the polyarylates, polyamides, polyetherimides, polysulfones and polycarbonates, epoxy resins and modified phenol-formaldehyde resins. Colorless and high purity bisphenol-A has to be used to produce high quality polycarbonates.
Polycarbonates are in turn essential engineering plastics. They have excellent resistance to high temperatures, high impact resistance and good insulation resistance. These polymers play a more and more important role in the industrial fields such as, for example, chemical, mechanical and electric/electronic engineerings. Recently, laser data storage discs have found widespread applications in the industries such as, for example, computer and video-audio industries since optical data storage techniques have a variety of tremendous advantages. The feedstock for the production of an optical data storage substrate must be a polycarbonate which is prepared by means of nearly colorless and ultrapure bisphenol-A (the content of bisphenol-A is higher than about 99.99% by weight). An ultrapure bisphenol-A not only has higher purity but also should satisfy the extremely strict standards with respect to color, transmisivity, ash and iron contents or the like. This raises higher requirements in relation to the synthesis and purification of bisphenol-A than the production of usual polycarbonate grade bisphenol-A.
Bisphenol-A is produced by the condensation reaction of phenol and acetone, using an excess of phenol, in the presence of an acidic catalyst optionally with a promotor. ##STR1## The reaction product mixture contains unreacted phenol and acetone, water formed during the reaction and by-products in addition to bisphenol-A.
The by-products which are formed during the condensation reaction of phenol and acetone include predominantly 2-(2-hydroxyphenyl)-2-(4-hydroxyphenyl)propane (hereinafter sometimes also simply identified as "2,4-BPA" or "o,p-BPA") and the Dianin's compound. Additionally, there are present in the reaction mixture small amounts of 2,4-bis [2-(4-hydroxyphenyl)isopropyl]phenol (hereinafter also sometimes identified as "triphenol"), polyphenol and some undesirable coloring substance. The presence of such by-products and impurities in a bisphenol-A product results in a decrease in the quality or performance properties of for example resins that are manufactured by making use of bisphenol-A.
In general, a process for the production of bisphenol-A comprises two essential stages, namely synthesis of bisphenol-A by means of the condensation reaction of phenol and acetone and subsequent purification of the resulting reaction mixture containing bisphenol-A.
The methods conventionally used in the synthesis of bisphenol-A include predominantly a "hydrochloric acid catalyzed method" and an "ion-exchange resin catalyzed method".
In the hydrochloric acid catalyzed method, hydrochloric acid as a catalyst is highly active and used in a small amount. The rate of the hydrochloric acid catalyzed reaction and the conversion of the starting materials, in particular acetone are high. However, the hydrochloric acid catalyzed method suffers from the disadvantages such as, for example, the strong corrosion of the acidic reaction solution on the apparatus used for the performance of the condensation reaction of phenol and acetone. Therefore, this process requires that the equipment for carrying out the condensation reaction and the subsequent treatments be made from particular types of materials. Additionally, the low selectivity of the reaction to the desired product and the decomposition of the obtained bisphenol-A are attributed to the presence of acidic substance during the distillation. Furthermore, a complicated purification installation is required for recovery of hydrochloric acid subsequent to the reaction and for purification of the obtained reaction product.
Moreover, the desired BPA product is susceptible to contamination. More importantly, all the equipment that is brought in contact with acidic substance must be made from special corrosion-resistant materials.
In some instances, sulfuric acid, sulfur compounds or other substances are employed as a cocatalyst or a promotor to improve the hydrochloric acid catalyzed method in some aspects but this has not overcome the disadvantages of the method for the production of bisphenol-A using an acid as a catalyst in general.
Alternatively, the ion-exchange resin catalyzed method employs a non-corrosive reaction system. Therefore, this method allows a variety of materials to be used for the manufacture of the reaction and successive treatment equipment and reduces in turn the expenditure of capital on the equipment to a great extent. Moreover, since an ion-exchange resin usable as a catalyst is generally insoluble in the reaction mixture system, it is easily separated after the condensation reaction and a quality bisphenol-A product can be thus obtained. In recent years, the conversion of the starting materials and selectivity to the desired bisphenol-A product have been improved to an important extent as the catalyst technology that is intimately associated with the ion-exchange resin catalyzed method advances continuously. As a result, this method is more and more extensively used in the synthesis of bisphenol-A. A great number of patents, patent applications and other publications have described the ion-exchange resin catalyzed method and in particular some of operation steps, specific resins and equipment used therein. For example, U.S. Pat. Nos. 3,073,868, 3,153,001, 3,172,916, 3,234,221, 3,873,275, 3,936,507, 4,054,611, 4,156,089, 4,209,646, 4,212,997, 4,215,011, 4,294,994, 4,308,404, 4,346,247, 4,354,046, 4,391,997, 4,400,555, 4,445,409, 4,471,154, 4,487,430, 4,492,807, 4,590,303, 4,740,634, 4,798,654, 4,847,433, 4,918,245, 4,950,806, 4,954,661, 5,087,767[also JP No. 64-332, 802(Kokai)], 5,105,026, and 5,124,265; GB 159,668, 1,183,564, 1,340,869 and 2,053,019; DE 2,733,537; EP 0,144,735A, 0,268,318A, 0,319,326A3[CN 1,034,361A and also JP No. 62-304,941(Kokai)], 0,324,080, 0,329,075, 0,330,146, 0,332,877, 0,343,349 and 0,442,122A; JP No. Sho 36-23,335(Kokoku), 38-1,368(Kokoku), 40-7,186(Kokoku), 47-43,937(Kokoku), 49-48,319 (Kokoku), 50-13,334(Kokai), 54-159,378(Kokai), 55-27,1 08(Kokai), 56-46, 831(Kokai), (Kokai), 57-88, 137 (Kokai), 60-122,004(Kokai), 61-78,741(Kokai), 62-148,441(Kokai), 62-178,532(Kokai), 63-56,335(Kokai) and 63-60,227(also CN 1,002,560C); SU 715,100 and CN 1,034,360A, 1,035,282A, 1,036,559A, 1,048,987A, 1,059,480A and 1,069,961 are concerned with the ion-exchange resin catalyzed methods more or less or some operation steps as well as the equipment and resin catalysts employed therein.
There have been proposed many processes for obtaining high purity bisphenol-A through the removal of the impurities or by-products which have formed during the condensation reaction.
In order to synthesize bisphenol-A in accordance with the ion-exchange resin catalyzed method, the following purification process is generally used: removing water, unreacted acetone and phenol from the liquid condensation reaction mixture by fractional distillation at a reduced pressure, then cooling the residual liquid mixture to precipitate bisphenol-A in the form of adduct crystals of bisphenol-A with phenol, further separating the resulting adduct crystals from the mixture containing by-products and impurities and finally removing phenol from the adduct crystals to obtain a high purity bisphenol-A product. Further, many processes are already provided for the treatment of the mother liquor from which the adduct crystals have been separated.
One of the methods for removing phenol from the adduct crystals of bisphenol-A and phenol is distillation method wherein phenol is distilled out at a reduced pressure. However, it is impossible to remove all the phenol present in the adduct crystals by making use of the distillation method. Therefore, it is necessary to perform a stripping step in a subsequent procedure as described in JP Nos. 47-43; 937(Kokoku) or 40-7, 186(Kokoku) or to conduct a recrystallization step with heated water as described in JP No. 57-88,137(Kokai).
More specifically, U.S. Pat. No. 3,049,569 to Francis N. Apel et al. describes a process for the production of ultrapure bisphenol-A comprising the steps of continuously contacting a mixture of acetone and excess of phenol with a substantially insoluble cationic exchange resin catalyst, separating the effluent from the reaction zone into two streams, isolating the reaction by-products and bisphenol-A from the first stream, dehydrating the second stream and recycling the reaction by-products, acetone and phenol which have been isolated to the reaction zone. According to Apel, a conversion of about 50% by weight is the most desirable since it provides yields of about 99% of the theoretical yield of bisphenol-A. The resulting reaction mixture contains only about 15% by weight of bisphenol-A. Therefore, the mixture must be concentrated and the recycle quantities are extremely large. Moreover, the purity in the order of about 99% is obtained (about 99.7% is obtained in the example).
U.S. Pat. No. 3,873,275 to Richard C. Bennett describes in general a crystallization apparatus and method wherein the mother liquor recirculation rate and the size of crystal particles removed through a fine crystal destruction circuit are independently regulated so that undesirable fine crystals removed from the slurry body undergoing crystallization and the residence time thereof are regulated to provide a product of substantially improved size uniformity. However, the Bennett apparatus is considerably complicated and the performance of the apparatus is difficult to be adjusted or controlled.
U.S. Pat. No. 4,209,646 to Caluire R. Gac et al. describes a process for purifying diphenylol propane (bisphenol-A) by preparing a liquid of from about 10% to about 50% by weight diphenylol propane, phenol and less than about 15% by weight of water at a temperature of from about 70.degree. C. to about 100.degree. C. and applying a reduced pressure such as from about 20 to about 120 mmHg thereto which corresponds to the vapor pressure of the mixture while simultaneously cooling the same to precipitate almost pure diphenylolpropane in the form of crystals. However, the obtained diphenylolpropane still contains up to about 2% by weight of impurities and the coloration of the diphenylolpropane crystals corresponds to 30APHA after melting.
U.S. Pat. No. 4,215,011 to Lawrence A. Smith, Jr. discloses a catalyst system for use in a reaction-distillation column comprising a plurality of closed cloth pockets containing a particulate catalytic material arranged and supported in said reaction-distillation column by a wire mesh that is intimately associated with said closed cloth pockets. This complicated arrangement of catalytic particles is particularly provided for use in the separation of isoolefins from streams containing mixtures of at least one isoolefin and the corresponding normal olefin. This patent is especially useful for the separation of isobutene from a stream containing normal butenes. It is not known to be useful or to have ever been used in the preparation of bisphenol-A.
U.S. Pat. No. 4,294,994 to Ming K. Li describes a method for removal of phenol from the adduct of bisphenol-A and phenol by subjecting the adduct feed at a temperature of from about 50.degree. to about 150.degree. C. to spray drying conditions such as at a temperature of from about 150.degree. to about 250.degree. C. with a small amount of liquid carrier having a boiling point below that of phenol and recovering the bisphenol-A product from the released phenol. The purity of the obtained bisphenol-A product, as shown in example 2 provided by Li, is up to about 99% by weight though it is obviously disadvantageous that the adduct of bisphenol-A and phenol experiences high temperature effect of up to about 250.degree. C. whereby degradation or undesirable reactions thereof usually occur.
U.S. Pat. No. 4,308,404 to Arien Kwantes et al. proposes an improved continuous process for preparing bisphenols such as bisphenol-A from phenol and acetone in the presence of an acidic ion-exchange resin catalyst in a reaction zone comprising a series of reactors wherein a part of the effluent from at least one reactor with the exception of the last reactor is recycled to the preceding reactor, preferably to the first reactor, and the ratio of the recycled stream to the stream fed to the following reactor (the recycle ratio) is in the range of from about 0.1:1 to about 10:1. Nevertheless, the Kwantes' manner of operation undoubtedly results in a substantial reduction in the reaction rate as the condensation reaction proceeds.
U.S. Pat. No. 4,351,966 to John W. Flock relates to a process for recovery of phenol from the tarry residue derived during the manufacture of bisphenol-A. According to Flock, the bisphenol tar is treated at temperatures of from about 200.degree. to about 500.degree. C. and atmospheric pressure to recover all of the trapped phenol and the phenol liberated from a variety of phenol-based compounds. Flock uses so-called molecular sieve catalyst, that is cryctalline hydrated silica-alumina catalyst.
U.S. Pat. No. 4,354,046 to Glem R. Ladewig et al. provides a process for improving the purity and yield of bisphenol-A by feeding the crude bisphenol-A containing any unreacted phenol and acetone as well as the water formed during the condensation reaction removed from the condensation reactor to a crystallizer, adding an organic solvent such as toluene and water, heating the resulting mixture to form a single liquid phase, cooling the liquid phase to obtain crystals of bisphenol-A, separating the solvent and water from the resulting mother liquor, mixing phenol with the mother liquor, contacting the mixture with a cation-exchange resin catalyst or hydrochloric acid to convert the impurities to bisphenol-A, removing phenol from the mixture and recycling the remainder and the separated phenol to the crystallizer and the condensation reactor, respectively. It can be obviously seen that the product yield of p,p-bisphenol and the conversion of the total impurities are about 95%, respectively.
U.S. Pat. No. 4,391,997 to Ashok K. Mendiratta describes a process for the production of bisphenol-A comprising reacting phenol and acetone in the presence of a cation-exchange resin as a catalyst in a continuous reactor system in which the reaction temperatures increases along the length of the reactor or alternatively, the reaction takes place in a series of reactors operated at progressively increasing temperatures to produce a condensation reaction mixture of bisphenol-A, phenol, acetone, water and phenol/acetone condensation reaction by-products which may be then treated by any conventional means to form a bisphenol-A product having limited quantities of coloring substance and other condensation reaction by-products or impurities. It is attempted according to Mendiratta's teachings to reduce the amount of by-products or impurities and the material losses, thereby improving the material usage and the quality of BPA in the system employed. However, the conversion and selectivity of the acetone reaction is also remarkably limited. Actually, at a phenol to acetone molar ratio of about 10.7:1 and the temperature of about 90.degree. C., the conversion of acetone remains constant at about 69%. Under steady operation conditions, p,p-bisphenol-A is formed in yields of about 94+ percent and p,p-BPA plus o, p-BPA are formed in combination in yields of from about 98+ to about 99+ percent (based on p,p-BPA, o, p-BPA and other minor by-products). The selectivity of p,p-BPA is believed to be possibly as great as only about 96% (based on p, p-BPA, o,p-BPA and other minor by-products).
U.S. Pat. No. 4,400,555 to Ashok K. Mendiratta provides an improved bisphenol-A synthesis reactor system using a multiple acetone injection technique in a cation-exchange resin catalyzed bisphenol-A production process. Ashok K. Mendiratta intends to yield high material usage and to improve bisphenol-A product color or hue as well as to reduce the equipment capital expenditure/operating costs involved with recovery and recycling of excess phenol for the same overall phenol to acetone ratio charged to the reactor system. In operation, 25-75% of the feedstream of acetone is injected to the first reactor or the beginning of the reactor and the remainder is injected to the subsequent reactors or along the length of the reactor and all of phenol is charged to the first reactor or the beginning of the reactor. It is believed that this procedure allows a high relative phenol concentration to be maintained during most of the condensation reaction process while the overall phenol to acetone molar ratio is reduced to be as low as possible. According to Mendiratta, the conversion and selectivity to p, p-BPA of acetone reaction are significantly limited [the yield of p, p-BPA is about 94+ percent and the yield of p,p-BPA and o,p-BPA in combination is only from about 98+ to about 99+ percent (based on p,p-BPA, o,p-BPA and other minor by-products)] by means of the multiple acetone injection system.
U.S. Pat. No. 4,471,154 to Frederick C. Franklin suggests a staged and fluidized bed distillation reactor including a reactor vessel containing a plurality of trays vertically spaced from one another and interconnected by means of respective downcomers for conducting reaction liquid downward from tray to tray, at least some of said trays further containing a quantity of a particulate catalyst which is confined within a containing volume by a screen in connection to each of the trays and fluidized by the action of vapor. When operation is started, a stream of vapor and a stream of liquid pass through the respective trays containing the catalyst thereon upward and downward, respectively. The lower and higher boiling materials are removed from the upper and lower portions of the distillation reactor, respectively. It is evident in view of teachings of Frederick C. Franklin that this patent is focused on conducting a reaction of reactants A and B by providing a staged and fluidized bed distillation reactor rather than on improving the purity and hue or color of a bisphenol-A product and at the same time simplifying the process for the production of bisphenol-A.
U.S. Pat. No. 4,492,807 to Viney P. Aneja suggests that up to about 15% by weight of water and up to about 15% by weight of an organic liquid be simultaneously added to a mixture comprising impure bisphenol-A and phenol. The organic liquid should not react with bisphenol-A or phenol and dissolves a substantial proportion of the impurities or by-products formed in the synthesis of bisphenol-A. Preferred organic liquids are toluene and acetone. The Aneja's invention is advantageous in that a pronounced increase in recovery of bisphenol-A such as up to about 90% recovery is obtained without a significant sacrifice in product purity. Obviously, the recovery and purity are not so improved as expected.
U.S. Pat. No. 4,590,303 to Ashok K. Mendiratta is concerned with a method for the preparation of bisphenol-A from phenol and acetone wherein from about 5% to about 70% by weight of acetone feed per hour based on the weight of total acetone feed charged to the condensation reactor per hour, preferably from about 10 to about 40% by weight is diverted and delivered to the rearrangement reactor so that the product distribution of the condensation reactor effluent is substantially maintained. It is reported that as a result of diversion of the total acetone feed to the rearrangement reactor, improved acetone conversion is realized and BPA productivity is enhanced. However, the highest overall acetone conversion is about 65% by weight, though there may be increase of about 35% in acetone conversion.
U.S. Pat. No. 4,740,634 to Isabel M. Gones de Matos et al. discloses a special aspect of the process for the preparation of bisphenol-A wherein water is added to the mixture comprising bisphenol-A, from about 0.5 to about 15 percent by weight of diphenol isomers and other impurities but essentially no phenol. The resulting mixture is brought to a temperature sufficient to melt the solid material present therein and then cooled to a temperature below about 90.degree. C. to form bisphenol-A crystals which are thereafter separated, washed and dried to obtain a bisphenol-A product. However, thus obtained bisphenol-A product has an initial absorbance of 0.111 and contains only less than about 99.5 percent by weight of p, p-BPA even if it is further purified by contacting with an organic solvent.
U.S. Pat. No. 4,798,654 to Shigeru Iimuro et al. teaches a process for preparing bisphenol-A comprising distilling the intermediate adduct of bisphenol-A and phenol at a temperature in a range from about 160.degree. C. to about 200.degree. C. in a dephenolization column, recovering phenol from the top of the distillation column and bisphenol-A from the bottom of the distillation column and recycling a part of bottom liquid to the adduct feed of bisphenol-A and phenol. It is said in the Iimuro disclosure that plugging of the distillation column is prevented and continuous operation for a long period of time such as one year is possible. However, the phenol content of the bisphenol-A product taken out of the bottom of the dephenolization column is still up to about 2%.
U.S. Pat. No. 4,847,433 Gaylord M. Kissinger provides a process for preparing dihydric phenols such as bisphenol-A which process is based on the finding that there are significant quantities of acidic impurities derived from the acidic ion-exchange resin catalyst in the stream which is recovered from the catalyst. These impurities are believed to cause the bisphenol-A product to disappear (breakdown). Therefore, Kissinger suggests that acid neutralizing effective amounts of a carbonate of a Group II--a metal or transition metal of oxidation number +2 be added with barium carbonate being particularly preferred. Data as to the purity of in particular bisphenol-A and the conversion of acetone are not found in the Kissinger's disclosure.
U.S. Pat. No. 4,918,245 to Shigeru Iimuro et al. describes a process for the preparation of bisphenol-A. According to '245, (1) one mole of acetone is reacted with 4 to 12 moles of phenol in the presence of a sulfonic acid type cation exchange resin catalyst modified with a mercapto group--containing compound such as mercaptoethylamine to convert from about 20 to about 60% of acetone, and (2) the reaction mixture containing unreacted acetone is successively reacted in the presence of the hydrochloric acid catalyst. However, the drawback of '245 is that the hydrochloric acid catalyst is used and even so the purity of the p,p-BPA thus obtained is only about 98.3% as shown in only one example of this invention.
U.S. Pat. No. 4,950,806 Shigeru Iimuro et al. describes a process for crystallizing an adduct of bisphenol-A with phenol from a phenol solution of bisphenol-A in the presence of water, said process comprising the steps of controlling the concentration of bisphenol-A in said solution by removing a portion of the phenol from said solution or adding phenol to said solution according to feedback control based on the measurement of solution density to obtain an adjusted solution containing from 20 to 50% by weight of bisphenol-A, and feeding the adjusted solution to the crystallizer to form a solution having a temperature of from about 35.degree. C. to about 70.degree. C. and maintaining the inside wall of the crystallizer at a temperature higher than that of the solution, provided the temperature difference is smaller than 5.degree. C. This patent is also disadvantageous in that hydrogen chloride is used as a catalyst and the reaction mixture issued from the reaction system must be concentrated.
U.S. Pat. No. 4,954,661 to Shigeru Iimuro et al. discloses a method for preparing high purity or high quality bisphenol-A by recovering in a high yield bisphenol-A from the mother liquor from which the adduct of bisphenol-A with phenol has been separated and removing coloring substances and other impruities. According to the first aspect of Iimuro's invention, a portion of the by-products which are not recovered as bisphenol-A are withdrawn from the reaction system with the same being prevented from recycling to any process or recycling the same to each process is minimized and therefore the bisphenol-A can not contaminated with such by-products due to the accumulation thereof. Furthermore, sinceall the withdrawn portions of the by-products which can be recovered to obtain bisphenol-A may be returned to the principal reaction process, it is possible to increase the productivity of each process to the maximum extent. This patent only teaches an overall process which involves operations such as concentration, crystallization and cleavage or cracking, etc. subsequent to the condensation reaction of phenol and acetone.
U.S. Pat. No. 5,087,767 to Kenichi Okamoto et al. suggests a method for preparing 2,2-bis(4-hydroxyphenyl)propane comprising reacting acetone and phenol in the presence of an acidic ion-exchange resin as a catalyst wherein the reaction of acetone and phenol is performed while removing a part of the water generated during the reaction from a mixed solution containing acetone and phenol by a pervaporation method with a selectively water-permeable membrane such as porous glass, silica, alumina and ceramic membranes. According to the method described in this patent, the water generated through the reaction can rapidly be removed simultaneously with or alternatively to the reaction by a pervaporation operation and, therefore, the catalytic activity of the ion-exchange resin is not impaired at all. Moreover, any complicated operations associated with dehydration are not required. Thus, the acidic ion-exchange resin catalyst can continuously be used over a long time period without any treatment for the regeneration thereof. Further, according to the method of this patent, bisphenol-A can be economically prepared from acetone and phenol in a high conversion rate and good yield. However, as shown in the illustrative examples, the capacity of removing water is not strong so that after about 8 hours of the condensation reaction in a batch stirred reactor the conversion of acetone or the yield of p, p-bisphenol-A amounts to about 75% for an inorganic-organic composite membrane, about 80% for an organic membrane and about 90% for an inorganic membrane.
U.S. Pat. No. 5,105,026 to Joseph B. Powell is concerned with improvements to the purity of a bisphenol product in a bisphenol by-product isomerization process wherein isomers of bisphenol are isomerized to the desired bisphenol product. During the isomerization, acidic resin fines elute from the acidic ion-exchange resin isomerization catalyst into the reaction effluent. These resin fines can be filtered effectively and without contamination by a bed of solid particles such as alumina or carbon. The removal of resin fines improves the product quality and yield by eliminating resin particulates and reducing acid catalyzed cracking of bisphenols during successive purification and finishing steps.
U.S. Pat. No. 5,133,942 Edward M. Jones provides an arrangement for concurrently carrying out chemical reactions in a distillation column reactor, separating by fractional distillation the reactants and reaction products, removing the reaction catalyst from a distillation column reactor and replacing the used catalyst with fresh and/or regenerated catalyst. The distillation column contains a plurality of suitable liquid-vapor contact trays. Each of said trays have a downcomer and weir associated therewith, said downcomer connecting each said tray to the tray below each said tray. A solid particulate catalyst is supported on at least a portion of said trays by wire mesh or screen or filter medium and submerged to approximately the depth of the liquid on said trays. The vapor rising through the liquid on the trays tends to keep the particulate catalyst in the form of suspension in the liquid. Obviously, there are a lot of chemical reactions which can not be carried out because the reaction temperature of the reactants and the distillation temperature of the component or product to be separated out by fractional distillation are not consistent with each other or there is a great difference therebetween.
EP 0,319,326A3 to Shigeru Iimuro et al. provides a process for preparing 2,2-bis (4-hydroxyphenyl) propane (also bisphenol-A) of high purity. Actually, Shigeru Iimuro et al. simply suggests a pretreatment step before the adduct of bisphenol-A with phenol, in particular that obtained by the condensation reaction of acetone and phenol and subsequent treatments such as, for example distillation or concentration and crystallizations of the resulting reaction mixture is subjected to the dephenolization operation. According to the Iimuro's invention, the adduct is washed with phenol which itself is obtained as a by-product when the adduct of bisphenol-A and phenol is decomposed to give a bisphenol-A product. It is reported in the Iimuro's description that the hue of bisphenol-A obtained by the decomposition of the washed adduct is about 10 APHA and the purity of the bisphenol-A product was believed to be satisfactory as a material for use in the manufacture of an optical storage polycarbonate. However, the purity of the bisphenol-A product is not specifically given in the Iimuro's disclosure.
JP No. 61-78,741 assigned to Mitsui Toatsu Chemicals, Inc. describes a process for the production of 2,2-bis (4-hydroxyphenyl) propane (BPA) wherein the mixed reaction solution containing phenol and acetone is brought into contact simultaneously or alternatively with an ion-exchange resin and a dehydrating agent. The provided examples as a consequence, reports that after about 8 hours of the condensation reaction in such a manner the conversion is at most about 95% and the purity of the obtained bisphenol-A product does not exceed about 97.5%.
CN 1,069,961A is directed to the preparation and purification of the adduct crystals of bisphenol-A and phenol, crystallization means and process for the preparation of a high quality bisphenol-A product. According to the teachings of this patent application, the reaction mixture issued from the condensation reaction of acetone and excess phenol is passed through a plurality of crystallization treatment stages and the adduct of bisphenol-A and phenol which is meanwhile crystallized and separated in the respective crystallization stages is brought into intimate contact with a phenol product which is already purified in accordance with a specific manner to wash and purify the adduct crystals thoroughly. Thereafter, phenol is removed from the adduct crystals by means of for example evaporation, extraction and steam stripping. It is asserted in the disclosure of this application that bisphenol-A having a high purity, a good hue (less than 15 APHA), good storage stability and resistance to coloration when it is melted may be obtained. Obviously, there is only stressed in the application the performance of the crystallization operation of the already formed adduct crystals of bisphenol-A and phenol rather than how to increase the purity of the obtained bisphenol-A through the improvements to various operation steps with a simplified reactor system and subsequent treatment means.
Although the bisphenol-A product obtained after the purification operations in accordance with the ion-exchange resin catalyzed method may meet the requirements as to the quality of bisphenol-A usable for the manufacture of conventional polycarbonates, there is heretofore unknown an ultrapure bisphenol-A product having a purity of such as, for example, more than about 99.95% or even about 99.99% sufficient for use in the manufacture of for example optical data storage materials.
Since the processes for the synthesis of higher purity bisphenol-A according to the ion-exchange resin catalyzed methods so far proposed in the literature such as in the above-mentioned patents and patent applications use higher molar ratios of phenol to acetone which is in general higher than about 8:1 and at the same time there are some limitations to the reaction temperature and residence time, etc., the concentration of bisphenol-A in the resulting liquid condensation reaction mixture is very low, typically below about 15%. Therefore, the liquid condensation reaction mixture must be concentrated before it is cooled to precipitate adduct of bisphenol-A and phenol in the form of crystals. Heretofore, there has been no proposal for omitting the concentration step since direct crystallization of the highly dilute condensation reaction solution undoubtedly results in very low yield of bisphenol-A and fully unacceptable color or hue of more than 15 APHA, thereby reducing the purity of thus obtained bisphenol-A product significantly. To concentrate the reaction mixture means that the process stream is subjected to strong thermal effect once more, thereby leading possibly to the decomposition or secondary reactions of the desired reaction product to form coloring substance because the liquid condensation reaction mixture from the reactor system contains slightly acidic impurities.
Moreover, the ion-exchange resin catalyzed methods as described in for example the above-mentioned patents or patent applications are still disadvantageous in that the condensation reaction rate is low and the residence time of feedstocks is long in the reactor system. The after treatment is complicated and highly loaded due to the high ratio of phenol to acetone and large amount of recycle unreacted phenol stream. In some instances, the reactor systems used are difficult to assemble or disassemble. For the bag construction as described in U.S. Pat. No. 4,487,430, some liquid may flow through the spaces between the bags.
Therefore, it is always desirable to further improve the conventional processes or some steps thereof in various aspects or further to develop novel processes for producing higher and higher quality (purity and coloration, etc.) bisphenol-A products to meet great demand in industrial applications although there have been a great number of processes for the production of bisphenol-A (BPA) which have shown separately some advantages over their respective preceding processes and have been described in a variety of patents and other publications such as those mentioned above.